Field of the Invention
The invention relates to a process for producing at least one structured metal sheet, a process for producing a laminated metal sheet pack and an apparatus for producing structured metal sheets. Such metal sheets are processed primarily to constitute honeycomb bodies for catalytic converters which are used in particular in motor vehicle exhaust gas systems. Such a honeycomb body is described, for example, in European Patent 0 245 737 B1.
Structured metal sheets are generally produced in the state of the art by shaped rollers which mesh with each other and which preferably have an involute tooth configuration or a tooth configuration of a similar construction. However, other geometries for the structures, for example a trapezium shape, a zig-zag shape, etc., are also known.
Portions are cut off the structured strip-shaped metal sheet and stacked to form a metal sheet pack, with a smooth sheet being inserted between the structured metal sheets. The ends of the stack are, for example, twisted in mutually opposite directions around at least two fixed points. The stack when deformed in that way is fitted into a tubular casing. The tubular casing, with the metal sheet stack fitted therein, is then subjected to a brazing operation in which the tubular casing with the metal sheet stack and the individual sheets are brazed together. The tubular casing and the metal sheet stack have different coefficients of thermal expansion. In order to ensure that a satisfactory brazed connection is produced between the metal sheets in relation to each other, and between the metal sheets and the tubular casing, it has already been proposed that the metal sheet pack be fitted into the tubular casing in a prestressed condition so that no gap formation occurs between the metal sheets and/or between the metal sheets and the tubular casing. In the case of honeycomb bodies which are wound in a spiral shape, it has already been proposed that radial depressions should be provided in the structured metal sheet at apex regions of the structure. The material serving for the welding or brazing operation can be disposed in the depressions.
The strip-shaped metal sheet experiences deformation during the structure-forming step. There are fluctuations in the height of the structure of the structured metal sheet due to fluctuations in the material properties of the metal sheet. Those fluctuations in the height of the structure are due to the fact that the elasticity of the metal sheet lies within a tolerance band. Tolerances with respect to the shaped rollers may possibly also be superimposed on that effect, so that there is no guarantee that metal sheet packs can always be fitted into a tube under the same prestressing. It has also been found that the cell density of a honeycomb body may also be different, with the same production process.
European Patent Application 0 279 159 A1, corresponding to U.S. Pat. No. 4,845,073, discloses a process for producing at least one structured metal sheet, wherein the structure is formed by inter-engaging toothed rollers.
European Patent Application 0 490 611 A1 also discloses a process and an apparatus for producing welded laminated metal sheets and packs of metal sheets.
European Patent Application 0 460 611 A1 discloses a structure-providing step through the use of which a first metal sheet is provided with a structure by using shaped rollers. A second, smooth metal sheet, is then applied to the structured sheet and the first and second metal sheets are passed through a second pair of rollers.